Mechanically controllable valve drive

ABSTRACT

A mechanically controllable valve drive includes a cylinder head, a valve lift adjustment device comprising a rocker arm, a pivoted lever assembly comprising an end surface, an engagement element, and a bearing means. The pivoted lever assembly is mounted in the cylinder head via the bearing means so as to be movable. A gas exchange valve is configured to have the pivoted lever assembly act thereon via the end surface. A positioning device is configured to engage on the rocker arm. A valve clearance is arranged between the rocker arm and the engagement element. At least one adjustment device is configured to provide a valve clearance adjustment. The engagement element of the pivoted lever assembly is operatively connected to the rocker arm of the valve lift adjustment device via a work curve.

CROSS REFERENCE TO PRIOR APPLICATIONS

This application is a U.S. National Phase application under 35 U.S.C. §371 of International Application No. PCT/EP2011/065048, filed on Aug. 31, 2011 and which claims benefit to German Patent Application No. 10 2010 048 708.2, filed on Oct. 19, 2010. The International Application was published in German on Apr. 26, 2012 as WO 2012/052217 A1 under PCT Article 21(2).

FIELD

The present invention relates to a mechanically controllable valve drive having a gas exchange valve onto which a pivoted lever arrangement acts via an end surface, wherein the pivoted lever arrangement is mounted in a movable manner in the cylinder head by bearing means, and wherein the pivoted lever arrangement has an engagement element which, via a work curve, is operatively connected to a rocker arm of a valve lift adjustment device. The present invention further relates to a mechanically controllable valve drive assembly.

BACKGROUND

Mechanically controllable valve drives of the above type have previously been described. DE 10140635 A1, for example, describes a mechanically controllable valve wherein a rocker arm is designed so that, by one end, it can be moved by means of a roll via a camshaft in a sliding block assembly and, by its other end, cooperates via a work curve with a pivoted lever so as to open and dose the gas exchange valve. In such a work curve, there is arranged, between the first roll and the work curve, a second roll which cooperates with an adjustable bar so that an adjustment of a valve lift position is made possible. In the valve, a spring means is further provided for biasing the rocker arm in the direction of the adjustable bar. DL 4326331 A1 describes a further valve drive having a lift adjustment device. This lift adjustment device also comprises a rocker arm which, via a work curve, cooperates with a pivoted lever and, via the pivoted lever, cooperates with a gas exchange valve. The adjustment of the rocker arm and thus the adjustment of the lift height here takes place, however, at the end of the rocker arm remote from the work curve. The camshaft engages a roll supported substantially at the middle of the rocker arm.

In order to accommodate wear effects of the valve seat and different operating conditions at different temperatures, valve drives are provided with a valve clearance which provide for a closed state of the valve throughout a certain driving cycle. More recent motors have so-called hydraulic tappets which not longer require a valve clearance and which provide that the valve drive is able to adapt to the respective operation and wear conditions. Hydraulic tappets of this type are used in combination with a spherical head having the pivoted lever supported thereon, also in valve drives with a lift adjustment device. Even though this provides an unobjectionable closing of the gas exchange valve, such measures have the effect that the point of attack of the work curve of the lift adjustment device onto the engagement element of the pivoted lever changes over the lifespan of the internal combustion engine. This in turn has the consequence that the valve lift adjustment position assigned to specified operational states no longer works precisely, which is particularly disadvantageous under the aspect of an optimal combustion and an associated low emission.

SUMMARY

An aspect of the present invention is to provide a mechanically controllable valve drive which avoid the above-mentioned disadvantages.

In an embodiment, the present invention provides a mechanically controllable valve drive which includes a cylinder head, a valve lift adjustment device comprising a rocker arm, a pivoted lever assembly comprising an end surface, an engagement element, and a bearing means. The pivoted lever assembly is mounted in the cylinder head via the bearing means so as to be movable. A gas exchange valve is configured to have the pivoted lever assembly act thereon via the end surface. A positioning device is configured to engage on the rocker arm. A valve clearance is arranged between the rocker arm and the engagement element. At least one adjustment device is configured to provide a valve clearance adjustment. The engagement element of the pivoted lever assembly is operatively connected to the rocker arm of the valve lift adjustment device via a work curve. Such a valve drive provides for an optimum combustion in a large variety of operational states by making it possible to newly adjust the valve drive after certain periods of time, such as during maintenance intervals. The wear of the valve lift adjustment device is further minimized by the fact that friction no longer exists in the base circle contact of the cam of the camshaft.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail below on the basis of embodiments and of the drawing in which:

FIG. 1 shows a schematic sectional view of a valve drive according to the present invention.

DETAILED DESCRIPTION

In an embodiment of the present invention, a mechanically controllable valve drive is provided by designing the valve lift adjustment device so that the rocker arm is movable by means of a roll via a camshaft in a sliding block assembly and pivotable by means of an adjustment member, wherein the side facing toward the pivoted lever comprises a work curve operatively connected to the engagement element, the rocker arm being biased by a spring member.

In an embodiment of the present invention, the rocker arm is designed in an L-shape having a work curve leg and a guide leg, wherein the positioning means are designed as a spring member having at least one spring force component in the direction of the guide leg. In an embodiment of the present invention, the spring member engages the work curve leg.

In order to create a valve drive which can also be used at highest rotational speeds, such as in motorcycles, and whish is thus also suited for highest specific cylinder performance with high valve acceleration, the bearing means can consist of a pivot bearing arranged on a pivot axis. By a bearing arrangement of this design, the high spring forces generated in such an application can be reliably accommodated.

In an embodiment of the present invention, the adjustment means can be provided between the gas exchange valve and the end surface. In such an arrangement, the adjustment means can be realized as adjustment disks of stepped thickness, said disks allowing for an extremely precise adjustment of the valve shaft.

There is also thereby provided a simple re-adjustment at certain maintenance intervals. The adjustment means for the valve clearance can further be provided in the pivot bearing, wherein the setting can he performed either exclusively thereby or in addition to the adjustment disks that are used. In order to accommodate extreme wear, for example, of the valve seat, and to also offer the possibility to re-adjust the engagement of the rocker arm with the valve lift adjustment device at maintenance intervals, it can be advantageous, apart from the above provision, if the adjustment means are provided in the valve lift adjustment device.

In an embodiment of the present invention, the pivoted lever assembly consists of a pivoted lever and a roll rotatably supported therein, said roll being operatively connected to the work curve of the rocker arm. In this arrangement, the pivoted lever assembly can be used as the adjustment means. In this case, a clearance adjustment can be performed by means of a simple classification of individual positions of the pivoted lever. The roll of the pivoted lever assembly can also he provided for use as the adjustment means.

In an embodiment of the present invention, the adjustment means can he realized by the adjustment member. It can further be considered realizing the adjustment means by the work curve of the rocker arm.

The work curve comprises different curve sections, such as, for example, for full stroke, partial stroke, idling and, of course, for the valve clearance. In an embodiment of the present invention, the work curve comprises two curve sections which allow for a valve clearance, one of the curve sections being assigned to a cold operating condition and the other one being assigned to a heated condition of an internal combustion engine. In this arrangement, the valve clearance can be adjustable in a temperature-dependent manner between the work curve and the engagement element by rotating the adjustment member.

It can also be provided that the adjustment means are realized by the sliding block assembly.

In an embodiment of the present invention, a valve drive arrangement is provided in that the rocker arms of adjacent valve drives are provided with guide rolls for guiding the rocker arm in a sliding block assembly, said guide rolls of two adjacent rocker arms being connected to each other via a stud axle, and a roll, engaging the camshaft, being arranged between said guide rolls.

The present invention will hereinafter be explained in greater detail with reference to the drawing.

FIG. 1 shows a mechanically controllable valve drive 2 comprising a gas exchange valve 4, partially shown, of an internal combustion engine, which is not shown in greater detail. The gas exchange valve 4 is shown as an example representative of a plurality of similar inlet valves of a cylinder of the internal combustion engine. The illustrated valve shaft of gas exchange valve 4 is engaged, in a known manner, by a pivoted lever assembly 6 via an end surface 9, so that the gas exchange valve 4 will be opened or closed in dependence on a camshaft 10. Said pivoted lever assembly 6 substantially consists of a pivoted lever 8 and a roll 12 rotatably supported therein. The pivoted lever 8 is further supported on a pivot axle 16 via a pivot bearing 14.

The roll 12, and thus the pivoted lever assembly 6, is in a known manner operatively connected to a rocker arm 18 and a valve lift adjustment device 20. In the illustrated embodiment, the rocker arm 18 is in an initial position determined by the closed gas exchange valve 4 (which is to say, valve stroke=0). In this initial position, there exists a predetermined clearance 22 between the roll 12 of pivoted lever assembly 8 and the rocker arm 18.

The rocker arm 18 is substantially L-shaped, Wherein rocker arm 18 comprises a guide leg 24 as well as a work curve leg 26 having a work curve 28 facing toward the pivoted lever assembly 8. in this arrangement, the valve lift adjustment device 20 is guided in a known manner by means of a guide roll 30 in a sliding block assembly 32. Reference is thereby made to DE 101 40 635 A1 where the configuration of an advantageous valve assembly is described. In this arrangement, the rocker arms of adjacent valve drives are connected by a stud axle which comprises a roll being engaged by a camshaft 10 with a corresponding cam 34 and initiating the corresponding valve stroke of the gas exchange valves.

A valve stroke adjustment is performed by the use of an adjustment member 36 via an eccentric member 38 engaging a further roll 40 of rocker arm 18. Depending on the adjustment angle φ of the adjustment member, there is reached a respective valve stroke height of the gas exchange valve 4 when the camshaft 10 is rotated.

For biasing the rocker arm 18 relative to the adjustment member 36 and for positioning the rocker arm 18 in the initial position, i.e., so that there is no engagement of the cam 34 of camshaft 10 and no engagement of the eccentric member 38 of adjustment member 36, a spring member 42 is provided which has a spring force component Fx in the direction of adjustment member 36 as well as a spring force component Fy in the direction of guide leg 24.

The above arrangement further allows for a considerable simplification of the assembly process for the described valve lift adjustment device because, in the initial state effected by the spring member 42, a contact exists between adjustment member 36 and further roll 40, between guide roil 30 and sliding block assembly 32, and between guide roll 30 and camshaft 10. In the shown embodiment, for setting the clearance, the pivoted lever assembly 6 can be lifted until it abuts on the work curve 28 of work curve leg 26. The distance between the valve shaft of gas exchange valve 4 and the end surface 9 of pivoted lever assembly 6 is then measured. A corresponding adjustment disk/setting disk 44 (shim) can now be selected whose thickness together with the desired clearance corresponds to the distance between the end surface 9 and the valve shaft of gas exchange valve 4.

It should be evident that, in case of a valve drive arrangement having two rocker arms whose guide rolls are connected to each other via a stud axle, with a further roll being arranged on the stud axle for cooperating with the camshaft 10, the positioning of the valve drive assembly is provided in that, due to the application of force of spring members 42 each acting onto a rocker arm 18 of the valve drive assembly, there exists a contact between the respective adjustment member 36 and the further roll 40 of a rocker arm 18, a contact between the respective guide rolls and the sliding block assembly 32, and a contact between the roll, supported centrally on the stud axle, and the camshaft 10.

The present invention is not limited to embodiments described herein; reference should be had to the appended claims. 

What is claimed is: 1-18. (canceled)
 19. A mechanically controllable valve drive comprising: a cylinder head; a valve lift adjustment device comprising a rocker arm; a pivoted lever assembly comprising an end surface, an engagement element, and a bearing means, the pivoted lever assembly being mounted in the cylinder head via the bearing means so as to be movable; a gas exchange valve configured to have the pivoted lever assembly act thereon via the end surface; a positioning device configured to engage on the rocker arm; a valve clearance arranged between the rocker arm and the engagement element; and at least one adjustment device configured to provide a valve clearance adjustment, wherein, the engagement element of the pivoted lever assembly is operatively connected to the rocker arm of the valve lift adjustment device via a work curve.
 20. The valve drive as recited in claim 19, wherein the positioning element is a spring element.
 21. The valve drive as recited in claim 20, wherein the engagement element is a roll, and further comprising, a camshaft, a sliding block assembly, and an adjustment member, wherein, the valve lift adjustment device is configured so that the rocker arm is movable via the roll and the camshaft in the sliding block assembly and to be pivotable via the adjustment member, wherein, a side facing the pivoted lever assembly comprises the work curve operatively connected to the engagement element, and wherein, the rocker arm is biased by the spring member.
 22. The valve drive as recited in claim 19, wherein the rocker arm is configured as an L-shape comprising a work curve leg and a guide leg, and the positioning device is a spring member comprising at least one spring force component in a direction of the guide leg.
 23. The valve drive as recited in claim 22, wherein the spring member is configured to engage on the work curve leg.
 24. The valve drive as recited in claim 19, further comprising a pivot axle, Wherein the bearing means of the pivoted lever assembly is a pivot bearing arranged on the pivot axle.
 25. The valve drive as recited in claim 19, wherein the at least one adjustment device is provided between the gas exchange valve and the end surface.
 26. The valve drive as recited in claim 25, wherein the at least one adjustment device is configured as an adjustment disk comprising a stepped thickness.
 27. The valve drive as recited in claim 24, wherein the at least one adjustment device is arranged in the pivot bearing.
 28. The valve drive as recited in claim 19, wherein the at least one adjustment device is provided in the valve lift adjustment device.
 29. The valve drive as recited in claim 19, wherein the pivoted lever assembly further comprises a pivoted lever and a roll rotatably supported in the pivoted lever, the roll being configured so as to be operatively connected to the work curve of the rocker arm.
 30. The valve drive as recited in claim 19, wherein the at least one adjustment device is the pivoted lever assembly.
 31. The valve drive as recited in claim 30, wherein at least one adjustment device is the roil of the pivoted lever assembly.
 32. The valve drive as recited in claim 21, wherein the at least one adjustment device is provided via the adjustment member.
 33. The valve drive as recited in claim 19, wherein the at least one adjustment device is provided via the work curve of the rocker arm.
 34. The valve drive as recited in claim 21, wherein the work curve comprises a first curve section and a second curve section which are configured to provide for the valve clearance, the first curve section being assigned to a cold operating condition of an internal combustion engine and the second curve section being assigned to a heated operating condition of the internal combustion engine.
 35. The valve drive as recited in claim 34, wherein the valve clearance is configured to be adjustable based on a temperature between the work curve and the engagement element by rotating the adjustment member.
 36. ne valve drive as recited in claim 21, wherein the at least one adjustment device is provided via the sliding block assembly.
 37. A mechanically controllable valve drive assembly comprising: a mechanically controllable valve drive as recited in claim 21; a plurality of gas exchange valves arranged in a row, the plurality of gas exchange valves comprising corresponding cylinders assigned thereto, each gas exchange valve having a respective mechanically controllable valve drive assigned thereto; a stud axle; a camshaft; a sliding block assembly; rocker arms comprising guide rolls, the guide rolls being configured to guide the rocker arm in the sliding block assembly, the guide rolls of two adjacent rocker arms being connected to each other via the stud axle; and a guide roll arranged between the guide rolls, the guide roll being configured to have the camshaft engage thereon. 